Group III-V semiconductor materials have been used in various electronic, optical, and optoelectronic devices. Examples of such devices may include metal-oxide-semiconductor field-effect transistors (MOSFETs), light emitting diodes (LEDs), laser diodes (LDs), etc. Group III-V semiconductor materials (i.e., a combination of at least one Group III material and at least one Group V material) may be fabricated by depositing, or growing, a stack of films of group III-V semiconductor materials on an underlying substrate, such as a silicon substrate. The stack of films may form active layers having certain electrical or optical properties via strain or gap engineering.
However, direct growth of certain group III-V layers on a silicon substrate has been problematic due to heteroepitaxial issues such as lattice mismatch, thermal expansion mismatch, and differences in interfacial surface energy between group III-V layers and the silicon substrate, which create dislocations that may propagate through the structure and degrade the device performance.
Additionally, silicon germanium strain relaxed buffers (SRBs) may be formed on active layers to provide a foundation. Active layers, such as channel layers, in transistor devices historically have been grown on silicon substrates. SRBs formed by existing methods on silicon substrates have defect densities greater than 10,000 cm−2 which cause defective channel layers to be grown thereon. Additionally, as dimensions have decreased, the need has been realized to provide SRB layers that provide a decrease in defect density and/or better absorb causes of defects.
Therefore, there is a need in the art for a method and apparatus for forming relaxed silicon germanium buffer layers on a substrate with improved quality and performance for advanced CMOS devices.